The body of an 11-year-old boy who was sucked into a storm water drain in the New South Wales Illawarra region has been recovered in a nearby creek bed.

Ryan Teasdale was last seen riding a bodyboard with his brother and friends in Riley Park in Unanderra on Thursday afternoon as torrential rain swept through the area. His brother raised the alarm about 4.30pm when he couldn’t find him.

His body was found after 11am on Friday at a creek bed at the end of a stormwater drain about 500 metres from the park.

“The family of the boy have been informed, and the family ask that their privacy be respected, and we are going to continue with our investigations at this stage,” Superintendent Zoran Dzevlan told reporters.

Earlier on Friday Dzevlan had told reporters: “What [the children] were doing was riding on boogie boards down the reserve, due to the rain, and what we believe may have happened is that Ryan may have fallen into one of those drains.”

More than 100 people including members of the State Emergency Service, NSW Police and council, marine rescue and ambulance had been involved in the search until about 1am on Friday. The search resumed again at first light in the area around Riley Park.

NSW State Emergency Service volunteers search a storm water drains around Riley Park in Wollongong on Friday morning. Photograph: Dean Lewins/AAP

The Illawarra region has been pelted with rain in recent days, and the SES warned residents to take care in floodwaters. Heavy rain has caused chaos up and down the coast.

Nine vehicles carrying 11 people were travelling on the Illawarra Highway at Macquarie Pass in torrential rain when a large amount of water flowed across the road, trapping cars on Thursday at about 5.30pm.

Police and the SES were able to free the first group at about 8pm, with the remaining group freed about an hour later.